【TIPS】MOJO TONEのフェイズ・インバーター記事の超ざっくり要約

皆さん、こんにちは。

こちらに、↑の記事で紹介したMOJO TONEのフェイズ・インバーターの記事について、超ざっくり要約を載せておきます。

（英語力がそれほど高くないのと意訳も入っているので、話半分くらいに読んでいただければと思います…）

パラフェーズ・フェーズ・インバーター（P.P.I）
スプリットロード・インバーター
ロングテールペア・フェイズ・インバーター
終わりに

パラフェーズ・フェーズ・インバーター（P.P.I）

Many guitar amps of the 1940s and ’50s—what we might call the earlier phase of the “tweed era”—used what’s called a paraphase (aka self-balancing) phase inverter. This PI, which comes in a range of varied but related forms, splits and inverts the signal just fine, but has difficulty delivering a very clean, linear load to the output tubes. Also, it tends to distort within itself at levels far short of what a larger set of output tubes, 6L6s for example, would otherwise be capable of achieving. As such, the use of a paraphase PI kind of self-limits the potential of any amp in which it appears. Sonically, it contributes to a vintage-leaning blues and rock ‘n’ roll tone, characterized by a smooth, early distortion with lots of compression, and some attenuation of both highs and lows, making it sound rather thick and midrangey. It can be a cool sound, for sure, but perhaps not for players demanding a broader vocabulary from their amps.
https://www.mojotone.com/blog/what-does-this-thing-do-phase-inverter

まず、1940年代から50年代にかけてのギターアンプでは、パラフェーズ・フェーズ・インバーターという方式の回路が多く使われていたそうです。

この回路では、それ自体が歪みやすいため、滑らかで、多くのコンプレッションを伴う早い段階からの歪み、高音域と低音域の両方の減衰などを特徴とし、かなり太く中域寄りのサウンドを作りだしていたとのこと。

スプリットロード・インバーター

This one will be far more familiar to players today than the earlier paraphase inverter, since the split-load network appeared in the legendary Fender 5E3 tweed Deluxe of the mid ’50s and onward, as well as its next-step-up siblings like the Pro, Super, Bandmaster, and low-powered Twin.
Although the phase inverter in the split-load design uses one triode to do this splitting and inverting—sending one leg of the signal from the plate and the other leg from the cathode—it is often coupled with a driver stage in front of it, and as such usually requires a full preamp tube. The split-load PI is capable of producing a sharper signal with a little better fidelity than the earlier paraphase PI, but when pushed hard it still folds into some distortion of its own, and therefore is still unable to push the output tubes to their own maximum potential before, and during, distortion. The distortion heard from the split-load PI is generally considered a little sweeter and richer than the paraphase’s distortion, and is a big part of the mid-sized tweed Fender sound. Even so, it doesn’t enable the full output tube crunch and roar we might be seeking.
https://www.mojotone.com/blog/what-does-this-thing-do-phase-inverter

次に、1950年代半ば以降、多くのギターアンプでスプリットロード・インバーターと呼ばれる、より効率的なフェイズ・インバーターが使われるようになったそうです。（Fender 5E3 Tweed Deluxeや、その次のステップのPro、Super、Bandmasterなど）

そのため、こちらの回路のほうが現代のギタリストには馴染みがあるだろうとのこと。

スプリットロード・インバーターでは、初期のP.P.Iよりも少し原音に忠実な信号を生成することができきるものの、プリアンプ段から強い出力を突っ込むとP.I自体がそれなりに歪んでしまうので、まだクリーン、クランチで出力管のポテンシャル一杯までの力を発揮させることは出来なかったそうです。

また、スプリットロード・インバーターで生じる歪みは、P.P.Iの歪みよりも少し甘く、リッチだと一般的には言われ、中型サイズのツイードフェンダーサウンドの大きな特徴となっているとのこと。

ロングテールペア・フェイズ・インバーター

For That, Makers Adopted The Long-Tailed-Pair PI In The Latter Part Of The Mid ’50s, And This Design Has Remained The King Of Inverters Ever Since.
This phase inverter requires the use of a full traditional preamp tube, two complete triodes. This provides one triode to deliver each half of the split signal, with a more complex network ahead of the tube to help achieve that splitting in the first place. This PI gets its name from the “tail” formed by the two-into-one resistors coming from the linked cathodes, as is visually evident on most schematic diagrams. In any case, the long-tailed-pair PI finally satisfied that quest for fidelity and power that obsessed so many amp designers in the late ’50s—when guitar-driven music was finding its way into bigger and bigger venues—and since then it has generally been considered the most efficient, linear, and balanced-sounding circuit for delivering a healthy signal to the output tubes.
Fender Took Up The Long-Tailed Pair In 1957 With The Arrival Of The 5F6 Bassman Circuit…
…after using the split-load PI on the previous 5E6 Bassman of 1956, and before. It was also used when the Twin upped its game to the so-called “high-powered” version, delivering about 85 watts from a quartet of output tubes, and somewhat counter-intuitively was adopted for later iterations of the dual-6V6 tweed Tremolux combo. Similarly seeking the most their output stages could deliver, Dick Denney and the folks at Jennings Musical Instruments used the long-tailed pair in all the most legendary early Vox designs of the late ’50s and ’60s. Of course, it also made its way to the Marshall JTM45 a few years later, and the renditions of the plexi that followed, via their emulation of the 5F6-A Bassman circuit. Following these classics, from the early ’60s onward the long-tailed-pair PI has been used in the majority of guitar-amp designs (other than, as before, those intentionally emulating specific vintage models that used other PI types), and is one of the most common elements connecting otherwise vastly different types of amps—found equally in the Mesa/Boogie Mark Series and Matchless Lightning, for example.
https://www.mojotone.com/blog/what-does-this-thing-do-phase-inverter

そして、その次に出てきたのがロングテールペア・フェイズ・インバーターという回路で、50年代半ばの後半から採用されて以降、今までのP.Iの中でも最も効率よくクリアな信号を出力段へ送るための回路だと考えられてきたとのこと。

このP.Iは50年代後半からFender、VOXなどの有名メーカーで採用され、60年代初頭以降もギターアンプ設計の大半に採用され、メサブギーのマークシリーズやマッチレスのライトニングなど、全く異なるアンプの共通点ともなっているとのこと。